Question

What is the value of unknown resistance R, of galvanometer shows null deflection in the given meter bridge set up shown in the fig?

• A. $97.50\Omega$
• B. $105\Omega$
• C. $220\Omega$
• D. $110\Omega$

Answer 1

Answer: (C)

$220\Omega$

Given that, the galvanometer shows null deflection. Hence the given combination is Wheatstone bridge.

Let $k$ be the resistance per unit length of the meter bridge wire.

Applying Wheatstone bridge principle we get:-

$\frac{20k}{55}=\frac{80k}{R}$

$⟹R=\frac{80\times 55}{20}=220\Omega$